Epoxides such as ethylene oxide and propylene oxide are important chemical intermediates. Propylene oxide is for example used as raw material for the production of polyether polyols, propylene glycol and glycol ethers. Ethylene oxide is for example used as raw material for the production of ethylene glycol, ethanolamines and acrylonitrile.
Epoxides are produced by epoxidation of olefins. Ethylene oxide is typically manufactured by direct oxidation of ethylene with oxygen. For propylene oxide, direct oxidation of propylene with oxygen has been proposed, for example in WO2009/120290. In practice, however, propylene is typically epoxidized to propylene oxide by reacting the propylene with an organic hydroperoxide, for example ethyl benzene hydroperoxide, tertiary butylhydroperoxide or cumene hydroperoxide. This is for example described in U.S. Pat. No. 3,351,635. An example of a commercially available epoxidation process that uses a hydroperoxide is the so-called SMPO process (styrene monomer propylene oxide process) wherein an ethyl benzene hydroperoxide is reacted with propylene to form methyl phenyl carbinol and propylene oxide. Methyl phenyl carbinol is subsequently dehydrated to styrene. Such process is for example disclosed in U.S. Pat. No. 5,210,354.
Conventionally, lower olefins such as ethylene and propylene are produced via steam cracking of hydrocarbon feedstocks including ethane, propane, naphtha, gasoil and hydrowax. An alternative route to lower olefins is the so-called oxygenate-to-olefin process. In such oxygenate-to-olefin process, an oxygenate such as methanol or dimethylether (DME) is provided to a reaction zone containing a suitable oxygenate conversion catalyst, typically a molecular sieve-comprising catalyst, and converted into ethylene and propylene. In addition to the desired lower olefins, a substantial part of the oxygenate is converted into C4+ olefins and paraffins.
In WO2009/065848 is disclosed an oxygenate-to-olefin process wherein the yield of lower olefins is increased by recycling a fraction comprising C4+ olefins to the reaction zone. At least part of the C4+ olefins in the recycle are converted into the desired lower olefins. A disadvantage of the process of WO2009/065848 is, however, that at least part of the recycle stream needs to be purged in order to avoid undesired accumulation of paraffins in the recycle stream. With the purge, also valuable C4+ olefins will be removed from the process without being converted into lower olefins.
Another disadvantage is that in an oxygenate-to-olefin process, less benzene is formed than in for example steam cracking of naphtha. If the lower olefins formed would then be converted into propylene oxide by an SMPO process, additional benzene would need to be imported and fed to the SMPO process.